1. Field of the Invention
The present invention relates to a printer and a printing method.
2. Discussion of the Background
Conventionally, Japanese Patent No. 3702711 discloses a printer using a collective head composed of a plurality of nozzle units. In this printer, the plurality of nozzle units are arranged, for example, such that at least one nozzle at the end of one nozzle unit and a nozzle at the end of other nozzle unit overlap in the direction intersecting the nozzle arrays.
There is a problem with the collective head that print quality can deteriorate at a boundary (seam) between nozzle units due to differences in assembling tolerance of the units. For this, in the printer of Japanese Patent No. 3702711, a raster is formed by mixing ink dots of the nozzle units at the overlapped portion of the nozzle units, thereby preventing the deterioration of print quality. The contents of Japanese Patent No. 3702711 are incorporated herein by reference in their entirety.
Recently, for satisfying the demand of increased printing resolution, a printer is sometimes employed which conducts printing on respective positions of a medium by means of multiple printing passes. As compared to a case using an inkjet head composed of a single head unit, for example, the aforementioned printing has larger possibility of producing black streaks as darker color portions than the other portions or white steaks as lighter color portions than the other portions at positions of boundaries of the printing passes. With such black steaks and/or white steaks, banding that is a series of bands running as trucks of printing passes occurs, thus deteriorating the print quality.